The researchers found that 278 (12%) adults reported at least 1 episode of buckling in the past 3 months. Of these, 13% fell during the episode. The frequency of buckling was similar both among men and women and among middle-age and older persons. Most persons were walking or climbing stairs when their knees buckled. Most people (217 people) reported more than 1 episode of buckling. Knee pain, quadriceps weakness, radiographic osteoarthritis, and limitations of physical function were more common among patients with buckling than among those who reported no buckling.